A standard power chuck of the type described in my U.S. Pat. No. 4,200,300 or in my applications Ser. Nos. 040,126 and 159,654 respectively filed on July 24, 1979 and June 16, 1980 has a chuck body that is rotatable about a chuck axis and that is formed with a plurality of angularly spaced and radially extending front guides and a plurality of angularly spaced and radially extending rear guides. Respective front jaw parts are radially displaceable in the front guides and project forwardly axially from the chuck body and respective rear jaw parts are radially displaceable in the rear guides. Means is provided including at least one operating element that is engageable with the rear jaw parts for radially displacing same jointly in the chuck body and the respective rear guides. In addition respective coupling members are engageable between the rear jaw parts and the respective front jaw parts and are each displaceable into a coupling position engaging both of the respective parts for coupling same together for joint radial displacement and a decoupling position for relative radial displacement of the respective parts.
The operating element of such a split-jaw chuck is normally connected to an actuator that is normally powered hydraulically. This actuator may be mounted directly on the back of the chuck or may be provided at some axial distance from it, in the latter case connected to the operating element by means of an appropriate tube.
In U.S. Pat. No. 3,369,464 of J. Blattry such an arrangement is shown wherein the actuator has a double-acting piston subdividing the chamber of the actuator housing into a pair of compartments which can be alternately pressurized and depressurized to displace the piston and the operating element linked to it. The actuator housing has an axially centered rearwardly projecting extension on which is fitted a connection collar having two alternately pressurizable hydraulic or even pneumatic connections. This collar can rotate relative to the extension so that as the chuck and actuator turn the collar stands still. Passages extending between appropriate locations underneath the collar and the compartments are provided with respective check valves of the so-called double type which are set up so that if one of the passages is pressurized, automatically opening the respective check valve, the other check valve will open to release pressure from the other respective compartment. These check valves are provided on the back of the actuator housing so that the entire assembly has a considerable overall length.
Commonly owned U.S. Pat. No. 3,641,875 of R. Kodalle shows another such arrangement wherein the check valve assembly is provided directly in the piston. The piston has an axially rearwardly extending stem formed with the passages which open at radially spaced locations aligned with inwardly open grooves of a collar that moves axially with this stem. To this end the actuator housing has a rear wall formed with a throughgoing hole provided with a seal through which the piston stem extends. This arrangement has the advantage of considerable simplicity, but nonetheless has an excessive axial length that takes up valuable space on a lathe. What is more, leakage problems around the rearwardly projecting piston stem are considerable.